Sprint Rear Wheel Cylinders - correct bore size?

[mikeybish]

Having taken 5/8" bore cylinders off the rear of my '76 Sprint (single circuit system) in the course of its restoration, the replacements that turned up in the post yesterday from a Triumph Parts supplier measured out at 3/4" bore.

A bit of research turned up the fact that several different suppliers/specialists are selling GWC1121 cylinders with differing bore sizes, worse still, they are specifiying a variety of sizes between them for the Sprint.

Probably this has been asked before, but here goes

"what is the correct rear wheel cylinder bore size for a Sprint?"

cheers

mikeyb

[trackerjack]

I think you will find that older than 76 have the larger ones and after that the 5/8 to keep it the same as the smaller Dollies!
However with some nice vented jobbies up front the rears are not going to be doing much.
As long as they are the same both sides I would not worry.
I replaced mine when one failed just to keep the constant maintainance down.

[Howard81]

I had an awful problem with this when I did the brakes on my 1500HL (late car, so has Sprint cylinders).

It turns out that the manufacturer of the parts has put the wrong partnumber on something, hence the confusion.

TD Fitchetts took my cylinders back and sent me a correct pair

[gmsclassics]

Checking that oversized rear cylinders are not fitted is critical to later Sprints with a tandem master cylinder. Too large a diameter and you run the real risk in the event of a front brake fluid leak / failure of not being able to push enough fluid through to activate the rear brake circuit fully.

I am using 11/16 inside diameter cylinders, having had to replace the previous 13/16 ones. While that difference doesn't seem a lot, it represents a 40% increase in area and volume of fluid to be moved to move the piston a given distance.

Geoff